The present invention relates to technologies for controlling the number of logical paths between a host computer and a storage system.
Technologies relating to computer systems containing a host computer and a storage system are disclosed for example in document 1 (U.S. Patent Application No. 2006/0026346), document 2 (U.S. Patent Application No. 2005/0120259), and document 3 (U.S. Patent Application No. 2006/0047930).
Document 1 provides disclosure in regard to determining paths giving consideration to loads on a host bus adaptor (HBA), a channel adaptor (CHA), and a logical unit.
Document 2 provides disclosure in regard to a configuration in which a host and a storage system are connected by multiple paths (multi-paths).
Document 3 provides disclosure in regard to managing logical volumes in levels and moving (migrating) data to logical volumes belonging to prescribed levels.
For example, as one example of the above-mentioned various computer systems there is a computer system in which a plurality of host computers (which hereinafter may be abbreviated to “host”) are connected to a same storage system. FIG. 31 illustrates one example of the computer system.
A storage system is provided with a high level storage device group and a low level storage device group for example.
The storage device groups are constituted by one or more storage devices. The high level storage device group is constituted by storage devices having high reliability or high performance for example, and the low level storage device group is constituted by storage devices having low reliability or low performance compared to the high level for example. By using the storage space of the storage device group it is possible to provide an actual logical volume (which hereinafter may be abbreviated to “VOL”).
The storage system has a plurality of interfaces to the hosts (which hereinafter may be abbreviated to “host I/F”) and a virtual logical volume (which hereinafter may be abbreviated to “VVOL”) is provided to each host. The host I/F may be ports for example or may be CHA provided with ports. Logical paths that pass through the host I/F span between the VVOL and the host computers and the VOL are mapped to the VVOL. For example, three paths span between the host 1 and the VVOL 1 via three host I/F A, B, and C and a VOL 1 is mapped to the VVOL 1. Furthermore, three paths span between the host 2 and the VVOL 2 via three host I/F B, C, and D and a VOL 2 is mapped to the VVOL 2. The host 1 can access the VVOL 1 via any path of the three paths that span to itself. When access is received to the VVOL 1, the storage system accesses the VOL 1 that is mapped to it. That is, access to the VVOL 1 involves accessing to the VOL 1. With this configuration, the hosts 1 and 2 are unaware of the VOL 1 and 2, and therefore it is possible for example to migrate the VOL 2 from the high level storage device group to the low level storage device group as shown in the drawing without being aware of the host 2.
Furthermore, with this computer system, the plurality of host I/F A to D can be shared between the plurality of hosts 1 and 2. In the example of FIG. 31, the host I/F B and C are shared between the hosts 1 and 2.
With this computer system, as shown in the drawing, access to the VOL 2, which is considered relatively unimportant compared to the VOL 1, can impose an adverse effect on the VOL 1.
That is, there can be conflict for access to the host I/F B and C shared by the plurality of hosts 1 and 2. For this reason, access to the VOL 1 and access to the VOL 2 affects each other. Furthermore, the level of importance of the VOL 2, which has been migrated from the high level storage device group to the low level storage device group, can be considered lower than the level of importance of the VOL 1 in the high level storage device group. In this case, when access to the VVOL 1 and access to the VVOL 2 are both conducted via the host I/F B or C, an adverse effect is imposed by access to the VOL 1 by access to the VOL 2, which has a lower level of importance than that of VOL 1.
There are techniques for avoiding access conflict based on the load of the CHA or the like, but these techniques give no consideration to the level of importance of the VOL and therefore they do not always enable such problems to be avoided.
The aforementioned problem is not limited to differences when the levels of importance of the VOL are different, but may also occur when other types of conditions of the VOL are different.